In the construction of buildings in earthquake prone regions, structures must be designed to withstand lateral forces and displacements due to seismic events. One design approach that has been increasingly utilized in multi-story buildings is to provide a coupled shear wall system. Various types of construction materials have been utilized in coupled shear wall systems. When such buildings include portions that are constructed from reinforced concrete, lengths of steel reinforcing “rebar” are normally used internal within concrete components. In such systems, the need arises for the use of a reinforced concrete coupling beam to span an otherwise open space between building components such as adjacent sheer walls. As an example, coupling beams are often utilized in the core structures of multi-story buildings to span between shear wall piers at the elevator or stair shafts. When coupling beams are employed, in many locales, various building codes dictate either the design requirements of such a component, or less commonly, the performance requirements of such a component, or in some instances, both. As a result, relatively complex and expensive designs have become the norm for multi-story building construction. The existing designs with which I am familiar are often relatively expensive to construct due to the labor intensive process of placing long inclined reinforcing bars through congested shear wall segments and coupling beams. Both the number of manhours required for construction personnel to install many components, as well as the relatively large quantity of reinforcing steel components, contribute to the cost. As a typical example, various building codes currently require the use of two intersecting groups of symmetrical diagonally placed reinforcing groups extending across the full length of the coupling beam, with the rebars adequately anchored within the adjacent sheer walls. While such prior art coupling beams, as well as other coupling beam designs, are currently available, and such designs vary in their effectiveness in resisting seismic events, especially as applied in the construction of multi-story buildings utilizing coupled shear wall systems.
By way of background, during a seismic event, the coupling beams of a coupled shear wall system are assumed to remain ductile and continue to dissipate energy well into the anticipated non-linear seismic building displacements as predicted by the various building codes, usually defined as either an earthquake having a 2% chance of excedence within a fifty (50) year period, or a an earthquake having a 10% chance of exceedence within a fifty (50) year period. Thus, in most multi-story buildings, especially mid-rise to high-rise buildings, the associated rotational demand or shear angle on the coupling beams in the coupled shear wall system will typically range in excess of about 5%, and sometimes may range from about 5% to about 6%. Thus, coupling beam designs should be able to withstand such demands while exhibiting stable hysteretic properties.
Since many buildings utilize coupled core wall systems, it would be desirable to achieve substantially equivalent or even better seismic performance results in coupling beams in coupled shear wall systems at reduced installed cost. Such cost reduction may be achieved by reducing the costs for labor and/or for components in such coupling beams, by reducing the shear wall thickness that is typically controlled by constructability requirements of the coupling beams, and by reducing the schedule length required for completion of construction of such components. Further, it would be advantageous, especially considering the relatively high value of a square foot of leasable or saleable floor space in many multi-story buildings, to reduce the “parasitic load” of unleasable or unsaleable floor space, by decreasing the floor space consumed by necessary shear walls in a particular building design.
Consequently, there remains a significant and as yet unmet need for a simple to construct, low material cost, and seismically effective coupling beam design adapted for use with multi-story buildings, such as high-rise offices, hospitals, or condominiums.
The foregoing figures, being merely exemplary, contain various elements that may be present or omitted from actual embodiments which may be implemented for a suitable coupled shear wall system in various buildings, depending upon the circumstances. Further, similar parts may be denoted with similar symbols, but utilizing a “prime” symbol as a suffix—“′”—and these shall be considered the functional equivalent of similar parts without such prime suffix symbols thereafter, as such nomenclatures is utilized in order to avoid unnecessary duplicate explanation of components or of the function thereof. An attempt has been made to draw the figures in a way that illustrates at least those elements that are significant for an understanding of the various embodiments and aspects of the invention. However, various other elements of a suitable coupled shear wall system may be utilized in order to provide a reliable, seismically functional coupled shear wall system that provides suitable lateral stiffness, strength, and ductility, and is thus resistant to shear forces when flexed during seismic events, by exhibiting stable hysteretic response and suitable energy-absorbing characteristics.